1. Field of the Invention
The present invention relates, in general, to polymers and, in particular, to polymers for use in electrochemical-based sensors.
2. Description of the Related Art
The use of electrochemical-based sensors that employ a redox mediator and a redox enzyme in conjunction with an electrode(s) for the determination of an analyte in a liquid sample has become of heightened interest in recent years. Such electrochemical-based sensors are believed to be particularly suitable for continuous or semi-continuous monitoring of analytes (such as glucose) in bodily fluid samples (e.g., blood or interstitial fluid samples). For example, electrochemical-based glucose sensors employing a redox mediator, a redox enzyme and a working electrode can determine (i.e., measure) glucose concentration using relatively low potentials (e.g., less than 0.4 V vs SCE), thereby limiting any interfering responses at the working electrode. For a further description of electrochemical-based sensors, see, for example, U.S. Pat. Nos. 5,089,112 and 6,284,478, each of which is hereby fully incorporated by reference.
In electrochemical-based sensors, the redox mediator facilitates electron transfer between the redox enzyme(s) and an electrode(s) of the electrochemical-based sensor. For electrochemical-based sensors that require long term stability, such as continuous or semi-continuous electrochemical-based glucose sensors, it is essential that the redox mediator does not leach away from the vicinity of the electrode. Therefore, it is not desirable to employ readily leachable redox mediators (such as readily leachable ferricyanide, benzoquinone and low molecular weight, quinone derivatives, ferrocene, low molecular weight ferrocene derivatives, ruthenium complexes and osmium complexes) in electrochemical-based sensors. In addition, if the redox mediator is a substance that is harmful to humans or other subjects, leaching of the redox mediator into a human's or other subject's body is undesirable and thus should be avoided.
To prevent redox mediator leaching, chemical compositions wherein redox mediators are chemically attached to redox enzymes have been proposed for use in electrochemical-based sensors. The redox enzymes of such chemical compositions can, however, suffer from a deleterious decrease in enzyme activity.
Alternatively, redox mediators have also been attached to water-insoluble synthetic polymer chains, such as polysilozanes, in order to prevent leaching. Such chemical compositions, however, suffer from low flexibility, and thus a reduced mediation activity, due to their hydrophobic nature. Redox mediators have also been attached to siloxane polymer backbones using hydrophilic eythelene oxide spacer compounds. Nonetheless, since each hydrophilic ethyelene oxide spacer compound attaches only one redox mediator to the siloxane polymer backbone, the mediation capability of the chemical composition is unfavorably limited. Furthermore, redox mediators covalently attached directly to hydrophilic polymer backbones are not suitable for efficient and secure attachment to electrodes of an electrochemical-based sensor.
Still needed in the field, therefore, is a chemical composition that can prevent the leaching of redox mediators from the vicinity of an electrochemical-based sensor's electrode while maintaining the redox mediator's activity. In addition, the chemical composition should provide for an efficient and secure attachment to an electrode of an electrochemical-based sensor. Also needed is an electrochemical-based sensor employing such a chemical composition.